Black knot

Black knot - Black knot
  • Latin name: Apiosporina morbosa (Schwein.:Fr.) Arx
  • French name: Nodule noir
  • Division: Ascomycota
  • Class: Pleosporales
  • Synonym(s): Dibotryon morbosum (Shwein.:Fr.) Theiss. & Syd.,
    Plowrightia morbosa (Schwein.:Fr.) Sacc.
Description

Micro-habitat(s)

Branch

Distribution

Eastern Canada

Damage, symptoms and biology

The name "black knot" aptly describes the most obvious sign of this disease: a rough black gall that can encircle the entire branch. Infection occurs during the spring, but the symptoms do not appear until the following spring. At that time, the bark on affected branches ruptures and a green liquid is expelled, and an olive-green swelling is formed. Over the summer, the gall turns a darker colour, eventually becoming black and hard. While the older parts of the gall die subsequently, the fungus continues to grow both around and along the affected branch. Large branches can resist the disease a long time after the infection begins, thereby supplying spores that enable continued spread.

Other information

Pruning off affected branches provides effective control, but it is important to carefully sterilize the pruning shear between every cut.

Canadian Forest Service Publications

Black knot

Information on host(s)

Main host(s)

Black cherry

Photos
  • Black knot Cherry tree bearing numerous black knots
  • Black knot Black knot
  • Black knot Canker on a branch
  • Black knot Black knot
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